This is a vintage Masonic ring, featuring a red synthetic ruby and a 10k yellow gold band with the Square and Compasses symbol.

Type: Vintage Masonic Ring

Materials: 10K yellow gold and synthetic ruby

Symbolism: Worn by Master Masons to signify loyalty to the fraternity

Historical context: Popular in the United States, especially during the 1940s and 1950s

The measurement across the band width is about 20mm which indicates it about a size 10. It’s can certainly be resized by a jeweler.